1. Field of the Invention
The present invention relates to a liquid crystalline compound, particularly a liquid crystalline compound having a tolan skeleton, which is very useful for the production of a retardation film or the like. The present invention also relates to a liquid crystalline composition containing the liquid crystalline compound and a retardation film having an optically anisotropic layer containing the liquid crystalline compound.
2. Background Art
Regarding a liquid crystalline compound having a skeleton such that two or more rod-shaped liquid crystalline compounds are linked in parallel, various reports have been made (see, for example, Background art 1: Senryo to Yakuhin (Dyes and Chemicals), Vol. 42, No. 4, page 85 (1997)). By linking two or more rod-shaped liquid crystalline compounds in parallel, the rod-like shape changes into an elliptical shape. This elliptical skeleton is considered important for exhibiting a biaxial liquid crystal phase. However, not only in such a skeleton but also in other various skeletons, the biaxial liquid crystal phase has been heretofore scarcely confirmed.
Also, studies are being made to apply a liquid crystalline compound to optical films such as retardation film by making use of its optical anisotropy. In this case, a polymerizable group is introduced into the liquid crystalline compound so as to suppress the flowability of liquid crystalline compound or increase the film strength. However, in the case of introducing a polymerizable group into a normal rod-like liquid crystalline compound, the polymerizable group is introduced into the side chain terminal of the rod-like liquid crystalline compound and therefore, a bifunctional polymerizable liquid crystalline compound mostly results. In order to overcome the problem of film strength at the application to a retardation film or the like, a trifunctional or greater functional polymerizable compound is necessary, but when a number of polymerizable groups is introduced into a rod-like liquid crystalline compound, the liquid crystallinity is lost and a desired optical anisotropy cannot be obtained. Accordingly, it is difficult in many cases to satisfy both the film strength and the liquid crystallinity. From such an aspect, development of a trifunctional or greater functional polymerizable liquid crystalline compound having a polymerizable group and at the same time, capable of exhibiting liquid crystallinity is demanded and several compounds have been heretofore developed (see, for example, Background art 2: JP-A-2001-233837 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”)).